1. Field of the Invention
The present invention relates to a transmission apparatus, sending apparatus, and receiver, and transmission method. In particular, this invention relates to a transmission apparatus, sending apparatus, and receiver, and transmission method preferably used for, for example, transmitting a digital audio signal regenerated by, for example, a digital audio apparatus to a speaker or headphone by way of infrared-rays.
2. Description of Related Art
In a conventional audio signal transmission device for transmitting an audio signal (aural signal) regenerated by an audio apparatus such as a CD (compact disc) player to other audio apparatus, for example, as speaker or headphone by way of infrared-rays, the CD player modulates the frequency of the audio signal to be transmitted, and an emitter is driven based on the resulting modulated signal. The infrared-ray corresponding to the modulated signal is emitted, the infrared-ray is transmitted in the space and received by an infrared receiver at the receiving side, for example, a speaker or a headphone. In the receiving side, the received infrared-ray is converted to a received signal corresponding to the above-mentioned modulated signal, and the original audio signal is regenerated by decoding the received signal.
Accordingly, an audio signal can be transmitted to a plurality of audio apparatuses simultaneously without physical transmission line by using the above-mentioned audio signal transmission device. However, in such audio signal transmission device, an audio signal is subjected to analogmodulation such as frequency-modulation, and such analog-modulation degrades signal-to-noise ration (S/N) of the audio signal in the receiving side if the transmission distance between the transmission side and the receiving side is far.
To avoid the degradation, recently the digital system in which an audio signal is digitally converted for transmission has been proposed. It is ideal that the ratio of data rate to transmission rate of a digital audio signal is one from the view point of transmission efficiency for using such digital system. However, because of the need for the transmission of error correcting code and other necessary data, the actual transmission rate is inevitably higher than the data rate for transmission of digital audio signals.
Accordingly, for improvement of transmission efficiency, the ratio of transmission rate to data rate of close to one is preferable, but if the ratio is complex, data processing may be complex for modulation and demodulation.
The transmission rate should be decided by taking both the improvement of transmission efficiency and the complex data processing into consideration.
Further, for example, since the frequency band permitted to use for transmission of audio signals by way of infrared-rays is specified by CP-1205 of EIAJ (Electronic Industries Association of Japan) and IEC (International Electrotechnical Commission)-1603, the transmission rate should thus be decided such that the transmission band used for the transmission is contained in these specified frequency bands.
The present invention is accomplished in view of these problems to perform not only efficient transmission by way of digital infrared-rays in conformity with specifications but also to suppress and minimize the complexity of data processing for modulation and demodulation.